1. Field of the Invention
The present invention generally relates to a refrigerant compressor and, more particularly, to a slant plate type compressor, such as a wobble plate type compressor, with a variable displacement mechanism suitable for use in an automotive air conditioning system.
2. Description of the Prior Art
A wobble plate compressor with a variable displacement mechanism suitable for use in an automotive air conditioning system is disclosed in U.S. Pat. No. 3,861,829 issued to Roberts et al. As disclosed therein, the compression ratio of the compressor may be controlled by changing the slant angle of the inclined surface of the wobble plate. The slant angle of the wobble plate is adjusted in response to a change in the crank chamber pressure which is generated by controlling communication between the suction chamber and the crank chamber.
In Japanese Patent Application Publication No. 60-135,680 corresponding to U.S. Pat. No. 4,586,874, the communication between the suction chamber and the crank chamber is controlled by an electromagnetic value which operates in response to an external signal, such as an electrical ON/OFF signal having a variable ON/OFF ratio. An ON signal and an OFF signal result in the communication between the suction chamber and the crank chamber being accomplished and being blocked, respectively. Therefore, when the communication between the suction chamber and the crank chamber is controlled with a high ON ratio signal, the crank chamber is substantially maintained at the suction chamber pressure, and thereby the compressor operation is maintained at maximum displacement.
Accordingly, when the electromagnetic valve receives a high ON ratio signal during operation of the compressor at an extremely high revolution rate, an unusually large decrease of the suction chamber pressure occurs such that frictional members of the compressor may be damaged. For example, seizure of the frictional members due to a large reduction of the lubricating oil flowing in the compressor may result.